This invention relates to centrifugal turbomachines, and more particularly to centrifugal fans.
The prior spiral casing which constitutes a housing of a centrifugal turbomachine is not symmetrical with respect to a rotation axis of an impeller, so that various outer end portions of the spiral casing are spaced differently from the rotation axis. This makes it necessary to install the casing by varying the height of the rotation axis depending on whether the discharge port of the casing is directed horizontally or vertically upwardly. Therefore, the following problems have been encountered.
A. Problems in Manufacture
(1) If belts of the same length for driving a centrifugal turbomachine are to be used, the position of an electric motor on the base must be changed. PA1 (2) When the electric motor is displaced on the base in the manner described above, the belt used must have its length varied in the event that the motor is located near the fan. To cope with this situation, belts of different lengths must be kept in stock and, moreover, the position in which the electric motor is installed must generally be varied. PA1 (3) In order to cope with these situations of Paragraphs (1) and (2), the base must be formed with several bores for bolting the machine in place, or bases for exclusive use with machines of different motor positions must be prepared. PA1 (4) If it is desired to make it possible to freely select the location of the electric motor, there must be provided an expensive slide base. PA1 (5) The height of the center line of the discharger port (which is generally aligned with the axis of the rotatable shaft) varies depending on the discharge direction. PA1 (6) To maintain the height of the axis of the rotatable shaft, it is necessary to vary the length of the leg portion of the spiral casing depending on the discharge direction of fluid: This results in preparing various types of legs, which are comparatively expensive. PA1 (1) Even if fans are of the same type and size, the height of the axis of rotation varies depending on the discharge direction, and at the same time the height of the suction port is changed. Thus piping must be changed accordingly. PA1 (2) The lateral sizes of the casing are variable depending on the discharge direction of fluid. This is inadvantageous in making effective use of the space available. PA1 (3) The layout of the fan and the arrangement of piping must be planned each time the discharge direction is varied. This is a troublesome process. PA1 (1) The casing varies in size depending on the size of the impeller. For example, in case fluid is discharged in the horizontal direction, the height of the center line of the discharge port varies depending on the size of the impeller, even if the height of the axis of rotation is fixed. As a result, the dimensions of the impeller (that is, the aerodynamic performance of the fan) become interrelated with the arrangement of piping and pressure loss, making design very complex. The layout of piping is troublesome for users. PA1 (2) In case the discharge direction of fluid is changed from the rightward horizontal direction into the leftward horizontal direction, the casing will have to be rotated through 180.degree. and at the same time the height of the center line of the discharge port is varied. To maintain the height of the center line of the discharge port, it is required to produce casings and impellers exclusively for use in discharging the fluid in the horizontal right direction and in the horizontal left direction. PA1 (3) Since the center line of the discharge port is offset from the axis of rotation, the discharge duct is generally bulky, thereby increasing a dead space which hampers effective utilization of the space of a room.
B. Problems in use
The above description is done with respect to centrifugal fans of belt drive type. It should be noted, however, that with centrifugal fans of direct drive motor type the height of the axis of rotation and the height of the center line of the suction port are generally varied depending on the discharge direction of fluid.
With fans having a prior spiral casing, the center line of the discharge port is not flush with the axis of rotation. For this reason, the conventional centrifugal fans have the following disadvantages: